1. Field of the Invention
This invention relates to lighting systems of a type comprising connectable unitary modular lighting assemblies, as employed to provide illumination in a wide variety of industrial, commercial, and consumer applications.
2. Description of the Related Art
Lighting systems of widely varying types are known in the art and in extensive conventional use. In many applications, lighting systems are employed which comprise modular lighting units including an elongate casing, e.g., in the form of an extruded tubular housing of resilient, translucent or transparent material (e.g. plastic tubing). Within the extruded tubular housing is a sequence of spaced-apart bulbs or other light emitting sources (such as LEDs, incandescent bulbs, or other electroluminescent lamps) in series and/or parallel relationship with one another. Lighting units of such illumination systems thus are provided in a unitary modular form, with the respective lighting units being interconnectable with one another, in series and/or parallel relationship, to form multi-unit extended lighting system assemblies for illumination of a specific environment or locus.
In parallel relationship arrangements of interconnected modular lighting units, means are provided for electrical communication of the illumination elements, usually disposed in serial relationship to one another in the interior of the housing of the strip lighting unit, with an exterior, and often remote, electrical (voltage) source, as well as with other lighting units. Such electrical communication is typically effected by means of alternating current (AC) conduction paths within the lighting unit. The AC conduction paths may be suitably coupled, e.g., co-linearly or coaxially, with an electrical connection line forming a connection between the AC conduction paths within the lighting unit. Multiple modular lighting units thereby may be deployed in parallel relationship to one another, or alternatively, series relationship arrangements of interconnected multiple modular lighting units may be conveniently fabricated and assembled.
One illustrative illumination device of the above general type is an electroluminescent light source, e.g., of a general type as broadly described in U.S. Pat. No. 5,051,654 issued Sep. 24, 1991 to Larry A. Nativi, et al., the disclosure of which hereby is incorporated herein by reference. Such electroluminescent light source may comprise a layer of electroluminescent phosphor material typically of a metal activated zinc sulfide fixed in place by a polymer binder between two conductive layers, one of which is transparent. When an alternating electric field is applied across the conductors, the phosphors are excited and emit photons with almost all of the radiated energy lying within the visible light spectrum. In such lighting units, the emission spectrum and wavelength generated by the phosphors is controlled by the activator element such as copper or manganese.
In the fabrication of such electroluminescent lamps, a conductive non-transparent sheet, e.g., of aluminum foil, is coated with an insulating layer of high dielectric constant material such as barium titanate. Next, an electroluminescent phosphor in a polymer binder is deposited over the dielectric layer and oven dried. A transparent conductive coating such as indium oxide or indium tin oxide, or an indium tin oxide sputtered Mylar film, then is deposited over the phosphor layer to form the front electrode of the lamp. A busbar having a conductivity greater than the conductivity of the transparent conductive coating is formed adjacent the periphery of the transparent conductive coating, and a thin nylon preformed film is applied over the busbar and the front electrode. The nylon film next is pulled up to position and attach the front lead and a second lead is attached to the aluminum foil conductive substrate. The entire assembly excluding a portion of the connecting leads then is sandwiched between two moisture barrier films such as polychlorotrifluoroethylene or polyester film, which are heat-laminated to the assembly and to each other around the periphery of the lamp.
Regardless of the specific form or type of illumination unit in a multi-unit lighting assembly, the resulting array of modular lighting unit(s) is disposed at a selected position in the specific environment or locus of use. For example, a length of the lighting assembly formed by an end-to-end series-connected plurality of lighting units, may be provided in a non-slip nosing structure extending across the front edges of the steps of a staircase, or mounted along a handrail or at the intersection of a wall and the floor in a hallway, thereby defining a directional path or boundary demarcation means. Another example is the provision of an illuminated path provided along the aisle and exits of an aircraft in the event of an emergency.
A wide variety of decorative and safety-enhancement uses for such lighting systems exists. Further, when the housings of the individual component lighting units in the assembly are of a deformable and flexible character, holding their shape and conformation as deformed, the resulting lighting assembly may advantageously be utilized in non-linear deployment applications, in which the "line" of the originally interconnected lighting modular units may be bent or deformed to a desired curvature or other non-linear conformation at the locus of use.
Although lighting systems of the aforementioned general type have been widely and successfully commercialized, such systems nonetheless suffer from various associated deficiencies which have limited their utility and applicability, as described more fully below.
Individual light source (illumination) elements in lighting systems are generally highly sensitive to variations of input voltage to the lighting modular unit containing such light source elements. In arrangements of lighting units in multi-unit system arrays, the failure of individual light source elements (generating short circuits) cause unsatisfactory fluctuations in voltage across the remaining light sources, often of a sufficient magnitude to render the unit at least partially inoperative.
Open circuit failures in a lighting module in a multi-module lighting system will break the circuit completely, and result in illumination failure.
Short circuits in a parallel arrangement of lighting modules will affect the voltage across all light sources in the system. The resulting voltage fluctuations and voltage level changes are often observable in the level (intensity) and consistency of the illumination provided by the lighting system, and may in the extreme diminish or even destroy the illumination capacity of sections or the whole of the lighting system.
The voltage sources and related voltage regulator circuitry incorporated into prior art designs of both the parallel and the series type have included only gross means for protecting the modular lighting units and resulting multi-unit lighting systems against short circuit failure of the light emitting elements therein. The conventional prior art practice has been to incorporate fuses into the power distribution system associated with the modular strip lighting units and resulting multi-unit lighting systems, thereby rendering entire series of light source elements susceptible to cessation of operation due to individual voltage (power) source failures.
A known alternative to such fused design utilizes a completely parallel circuitry in which each light source element is individually connected to the common voltage source power supply means, and each individual light source element/power supply means connection has its own separate fuse. Such a solution, however, is impractical for the reason that its implementation undesirably increases the cost, complexity, and size of the lighting system.
In addition to installational/operational difficulties, previous modular lighting systems have entailed mechanical design deficiencies which have adversely affected their implementation and use. In particular, although electroluminescent lamps have been in extensive use for a long period of time, the present practice to protect the power distribution system providing power to the electroluminescent lamp array has been to incorporate a fuse into the distribution system to prevent the occurrence of electrical overload conditions especially during short circuit failures of individual electroluminescent lamp elements in the lighting array. Another method of protecting the electroluminescent lighting system from overload incident to lamp failure which has been utilized in the prior art is the powering of each lamp off an individual power circuit which is protected by a fuse. While these approaches do work, they increase the complexity of the lighting system and restrict product applications in instances where individual fusing needs to be simple and inexpensive.
Accordingly, it would be a significant advance in the art, and is correspondingly an object of the present invention, to provide a lighting system, and modular lighting units therefor, which overcome the aforementioned deficiencies of the prior art, and provides a simple, ready and economical lighting unit protected against electrical overload conditions, e.g., overload conditions caused by failure of individual lamp elements in a multi-element lighting unit.
Various objects, advantages and improvements of the present invention will be more fully apparent from the ensuing disclosure and appended claims.